As the human genome project nears completion attention is returning to the gene products, most of which function by interacting with other gene products or with ligands. Thus an understanding of function usually requires an understanding of the various interactions that a protein engages in. Biosensor technology offers one of the most powerful approaches to detecting and characterizing protein-protein interactions. Here we request funds to purchase a Biacore model 3000 to facilitate studies of a variety of interactions of blood and matrix proteins and their receptors. Five major users will investigate molecular interactions of fibronectin (Ingham), fibrinogen (Medved), coagulation factor VIII (Saenko), plasminogen activator inhibitors (Lawrence), and members of the low-density lipoprotein receptor family (Strickland). One minor and one major user will also use the instrument to help identify ligands for transmembrane receptors. A second minor user will use the instrument to characterize ligand interactions with integrin alphaMbeta2. The availability of this instrument will greatly enhance the ability of these NIH-funded investigators to achieve their aims and will accelerate the development of knowledge required to better understand a variety of pathologies.